With the increasing of energy consumption, the requirements on energy saving are getting higher and higher. The illumination consumption is an important part of the energy consumption. LED illumination, as an energy saving and green illumination, will replace the traditional gas discharge lamps and the incandescent lamps. LED has the advantages of long life, high luminous efficiency, and energy saving besides which, its simplicity in driving and controlling of the LED makes it easy and flexible to adjust the illumination intensity, which is particularly suitable in the situation when we need to adjust the illumination intensity according to the different conditions. For example, in the road illumination, the plaza illumination and other outdoor or indoor illumination, when there is no need for 100% illumination intensity, dimming can save a lot of energy.
Since the LED power supply is the AC/DC switching power supply with high efficiency and wide input voltage range, the traditional dimming mode such as controlling input voltage or phased angle, can not adjust the output voltage or current, and can not achieve the purpose of illumination intensity adjustment of LED. Currently, there are a variety of driving circuits for dimming. In some circuits, the automatic timing dimmer is added to the LED driver, which means the lighted LED will be dimmed after a fixed time period. This kind of dimming circuit is under the control of timing dimming circuit and built-in device for detecting illumination intensity, which can not be controlled flexibly. In some other circuits, a control circuit is added to the LED driver in order to receive the radio signal or the power line carrier signal sended by controller, and the signal is used to control the illumination intensity of LED. But the shortages of this mode are expensive cost, complex circuitry, and low reliability (shown in FIG. 1).